50mJ超短脉冲KrF激光系统的参数优化

 介绍了原子能院建立的钛宝石/KrF混合型激光装置，主要输出参数的测量和性能优化。放电泵浦准分子激光器采用离轴放大结构，结合棱镜对进行GVD补偿，获得50mJ，220fs的紫外超短脉冲。用40cm透镜聚焦，靶上功率密度达到10¹⁷ W/cm²。     

超短超强激光对比度的测量研究

 为了准确地确定飞秒激光对比度的信息，基于两束不同激光的互相关原理，利用非线性晶体对激光强度变化十分敏感的特性，研制了一台三阶相关仪，并用其对钛宝石激光放大系统输出的飞秒激光脉冲进行了测量，得到了有关该系统的强度对比度的信息。结果显示：该系统输出的激光对比度在10⁶左右，在脉冲的前沿和后沿有很强的ASE辐射，并且延续了很长的一段时间；种子脉冲的对比度在10⁵左右，而且在主脉冲前约2ps的位置上，有一个强度很低的小脉冲，在主脉冲的两翼各有一个非常小的台阶。     

Gires-Tournois干涉镜补偿色散的自启动飞秒Cr4+:YAG激光器实验研究

利用一片GTI镜补偿腔内色散,并使用宽带半导体可饱和吸收片,实现了锁模自启动的飞秒Cr⁴⁺:YAG激光输出.在9W平均功率的1030nm激光抽运下,获得输出脉冲功率为95 mW,光谱半高全宽45 nm,中心波长1508 nm,实测脉冲宽度为65 fs.     

可编程声光色散滤波器在10 Hz飞秒再生放大系统中的应用

报道了在10 Hz飞秒再生放大超快激光系统中,运用可编程声光色散滤波器(AOPDF)对注入再生放大的种子光进行频谱整形和色散预补偿,使钛宝石激光系统输出光脉冲谱线半峰全宽由原来的38 nm展宽到66 nm,压缩后输出脉冲宽度从35 fs减小到20 fs。实验结果表明,利用可编程声光色散滤波器能够同时独立进行光谱整形和大范围内色散补偿的特性,可以有效抑制啁啾脉冲放大过程中存在的谱线增益窄化效应,补偿钛宝石激光系统中存在的残留色散。这为进一步研制小于20 fs,10 TW量级钛宝石激光系统奠定了基础。     

交叉偏振滤波技术提高飞秒超强激光信噪比的研究

对交叉偏振波滤波技术理论分析的基础上,在"极光-III"装置中采用该技术进行了钛宝石飞秒放大激光脉冲对比度提高的实验研究,不仅显著的抑制了纳秒范围内再生放大器产生的预脉冲,而且也将皮秒范围内的信噪比由10^-5提高到了10^-7,实验测得基波到交叉偏振波的转化效率大于10%.研究表明,该技术可以有效地提高飞秒超强激光的信噪比.     

20TW超短脉冲激光装置的研制

 介绍了基于啁啾脉冲放大技术的20TW全钛宝石超短脉冲激光装置的研制。该装置的主放大器采用全像传递的空间四程放大构型，可以保持良好的近场分布和提高能量转换效率。主放大器的钛宝石晶体为30mm×15mm，6台调Q倍频的YAG激光器泵浦。压缩后脉宽50fs，能量1J，峰值功率可达20TW，聚焦功率大于3×10¹⁸W/cm²。     

宽带自锁模钛宝石飞秒激光脉冲的实验研究

在线性Z形折叠腔的基础上,采用了一种能够消除输出耦合镜带宽限制的方法,用3mm的钛宝石短晶体和石英色散补偿棱镜得到了光谱带宽为121nm的自锁模钛宝石激光脉冲.在分析光脉冲自相关仪测量系统对测量影响的基础上,优化并基本消除了测量系统带来的影响,假设光脉冲形状为双曲正割型,得到了12fs的光脉冲,该光脉冲光谱半宽(FWHM)为87.6nm,中心波长为849.7nm,光脉冲平均输出功率为400mW,重复率为97MHz.     

输出能量4mJ的1kHz飞秒掺钛蓝宝石激光再生放大研究

针对高能量千赫兹重复频率飞秒激光的应用需求,设计了一套采用线性再生腔结构的高效率飞秒钛宝石激光啁啾脉冲放大系统.通过优化腔型设计,在重复频率为1 kHz、单脉冲能量为20 mJ的527 nm激光抽运下,将展宽后的800 nm啁啾脉冲激光的能量放大到5.8 mJ,对应斜效率达到30.7%.进一步通过色散补偿压缩脉冲宽度,获得了单脉冲能量为4 mJ、脉冲宽度为45.7 fs的输出,稳定性测量表明激光的能量抖动仅为0.18%(均方根值).     

两级钛宝石激光系统放大实验

 用两级多程放大构型进行了钛宝石脉冲激光的多程预放大和功率放大实验, 以倍频YAG为泵浦源, 当注入光能量为1nJ时输出脉冲能量达23mJ, 放大总增益大于10⁷。     

单脉冲飞秒激光时域参数测量技术研究

钛宝石飞秒激光放大系统具有重复频率低、脉冲波形复杂等特点，为准确测量其峰值功率，提出对单次脉冲波形和脉冲宽度测量的需求。介绍了单脉冲飞秒激光时域波形和脉冲宽度的测量原理和测量方法，设计了基于频率分辨光学开关法的单脉冲飞秒激光时域参数测量装置。讨论了单脉冲飞秒激光时域参数测量校准面临的问题及解决方法。     

Generation of high-contrast and high-intensity laser pulses using an OPCPA preamplifier in a double CPA, Ti:sapphire laser system

We demonstrate a high-contrast, high-intensity double chirped-pulse amplification (CPA) Ti:sapphire laser system using an optical parametric chirped-pulse (OPCPA) pre- amplifier. By injecting cleaned microjoule seed pulses into the OPCPA, a temporal contrast greater than 10¹⁰ within picosecond times before the main femtosecond pulse is demonstrated with an output pulse energy of 1.7 J and a pulse duration of 30 fs, corresponding to a peak power of 60 TW at a 10 Hz repetition rate. This system uses a cryogenically-cooled Ti:sapphire final amplifier and generates focused peak intensities in excess of 10²⁰ W/cm².     

14-fs high temporal quality injector for ultra-high intensity laser

We present a chirped pulse amplification (CPA) Ti:Sa laser generating sub-15 fs pulses with expected high temporal quality. Gain-narrowing in the pre-amplifier is balanced by a variable spectral reflectivity mirror and by a fine adaptation of the saturation conditions. A crossed polarized wave generation (XPW) filter is introduced to enhance the contrast, reduce the pulse duration and improve the spectral quality. The pulses are generated at 10 Hz repetition rate, with pulse energy of 110 μJ and very clean Gaussian spectrum. The temporal contrast is evaluated by a measurement before the XPW filter and calculations of the enhancement by the filter. The potential temporal incoherent contrast is 10¹² and the coherent contrast 10¹⁰. The performance of the system makes it suitable as an injector for petawatt lasers operating in the double-CPA scheme.     

Influence of spectral phase on cross-polarized wave generation with short femtosecond pulses

In this paper we present the first comprehensive study of the role of spectral phase on cross-polarized wave (XPW) generation using sub-30 femtosecond (fs) laser pulses. XPW generation improves the temporal contrast and shortens the pulse duration of fs chirped pulse amplification (CPA) lasers. For Ti:Sa lasers, compression below 30?fs is non-trivial and therefore never perfect. We therefore systematically analyze the effect of an arbitrary input spectral phase on the output spectrum and efficiency of the XPW process, both theoretically and experimentally. We derive the maximum acceptable value of residual phase for a given initial pulse duration in order to efficiently drive the XPW process for pulse shortening and contrast improvement.     

A double-pass optical parametric amplifier seeded by a blue-shifted output of a photonic-crystal fiber

A blue-shifted output of a photonic-crystal fiber, providing a frequency upconversion of femtosecond Ti:sapphire laser pulses, is used to seed a double-pass optical parametric oscillator (OPA). The OPA is based on a BBO crystal, pumped by 65-mW 150-fs second-harmonic pulses of a Ti:sapphire laser. Gain factors in excess of 10³ are demonstrated for such an OPA, yielding tunable light pulses within the range of wavelengths from 420 to 650 nm, a peak power up to 250 kW, and a typical pulse width of about 200 fs at a repetition rate of 100 kHz. PACS 42.81.Gs; 42.81.Qb     

Spectral-Phase-Modulated Cross-Polarized Wave for Chirped Pulse Amplifier with High Contrast Ratio

We demonstrate a high-quality cross-polarized-wave filter based on spectral phase modulation. Driven by wellcompressed spectral-phase fully-compensated fundamental laser pulses, the filter stretches the pulse bandwidth from 35 nm to 70 nm with a conversion efficiency of 20%. After implementing the filter into a femtosecond TW Ti:sapphire laser system, we generate 40 mJ output pulse energy with pulse duration of 18.9 fs. The temporal contrast of the compressed pulse is enhanced to 10~9.     

飞秒超强激光多通预放大过程中的脉冲信噪比研究

从啁啾脉冲放大的基本理论出发,详细计算了啁啾脉冲在多通预放大中各个时间点的增益情况,并设计了一个十通预放大器进行了实验研究. 结果显示,在抽运通量为1.6 J/cm²的非饱和放大情况下,种子脉冲经过十通预放大之后信噪比由10^-5提高到10^-7. 这表明在非饱和抽运通量下,多通预放大器可以有效提高激光脉冲的信噪比. 关键词： 多通预放大 信噪比 飞秒钛宝石激光器     

10(-10) temporal contrast for femtosecond ultraintense lasers by cross-polarized wave generation

We take advantage of nonlinear properties associated with chi(3) tensor elements in BaF2 cubic crystal to improve the temporal contrast of femtosecond laser pulses. The technique presented is based on cross-polarized wave (XPW) generation. We have obtained a transmission efficiency of 10% and 10(-10) contrast with an input pulse in the millijoule range. This filter does not affect the spectral shape or the phase of the cleaned pulse. It also acts as an efficient spatial filter. In this method the contrast enhancement is limited only by the extinction ratio of the polarization discrimination device.     

Generation of 7-fs laser pulse directly from a compact Ti:sapphire laser with chirped mirrors

A compact femtosecond Ti:sapphire laser resonator consisting of three chirped mirrors and one output coupler was designed. By accurately balancing the intra- cavity dispersions between Ti:sapphire crystal, air and chirped mirrors, we directly generated the laser pulse shorter than 7 fs at the average power of 340 mW with 3.1 W pump. The repetition rate of the laser oscillator is 173 MHz at the centre wavelength of 791 nm, and the ultrabroaden spectrum covers from 600 nm to 1000 nm. To the best of our knowledge, this is the simplest laser resonator capable of generating sub-10 fs laser pulse.